Generally, a capacitor constitutes a unit cell of a semiconductor device together with a metal oxide semiconductor (MOS) transistor, providing a function of frequency modulation. As shown in FIG. 1, such a capacitor generally has a structure in which a bottom electrode 12, a dielectric layer 14, and an upper electrode 15 are successively formed on a semiconductor substrate 11. Recently, with a refinement of a design rule for semiconductor devices, the area occupied by the capacitor in the semiconductor device is reduced to enable the fabrication of a capacitor with a large capacitance in a reduced area. However, the conventional capacitor shown in FIG. 1 has a structure in which the bottom electrode 12 is formed in a planar shape, which limits the maximum capacitance that may be employed in a micro or semiconductor device.
To satisfy the need for a capacitor with large capacitance, at least one study has concentrated on development of a capacitor having increased capacitance in a unit area. As a result, as shown in FIG. 2, a method of maximizing a capacitance of capacitor in which a bottom electrode 22 has been formed as an uneven shape to increase an effective area contacting with a dielectric layer 23 has been proposed. In addition, a method of maximizing a capacitance by use of various capacitor structures has also been provided. However, because the conventional capacitor has a fixed capacitance, regardless of its capacitance level, it has a problem in adapting to a presently used semiconductor device having a multi-function.